Process for demetallizing metallized paper



Feb. 3, 1948. R. A. GROUSE 2,435,441

PROCESS FOR DEMETALLIZING METALLIZED PAPER Fil ed Oct. 20, 1943 ssheets-sneak 1 Feb. 3, 1948. R. A. GROUSE PROCESS FOR DEMETALLIZINGMETALLIZED PAPER Filed Oct. 20, 1943 3 Sheets-Sheet 2 27v ve/vToR x N QFeb; 3 v 'PROCES'S FOR DEMETALLIZING' METALLIZED PAPER R. A. GROUSE 3Sheets-Sheet 3 IN van/70R Filed Oct. 20, 1943 Patented Feb. 3, 1948UNITED STATES PATENT DFFICE PROCESS FOR 'DEMETAILLIZING METALLIZED PAPERRichard Alfred Grouse, London, England, assignor to A. H. Hunt Limited,London, England, a company of Great Britain ApplicationOctober 20, 1943,Serial No. 507,042 In 'Great Britain October 23, 1942 to constitute a:condenser'providing at least one margin oneach of thestrips is-free ofmetal. It is :necessary that the margin should be free of metal in orderto ensure that there is no flash over .or short circuit from oneelectrode to the other and the dhigherthe voltage (at which'thecondenser is to beused-the wider mustthe margin be. However, intheinterests of compactness the margin should be kept at a minimum valuewhich issuitable for the working voltage at which the condenser isintended to be employed; this, of course, implies that the flash-overvoltage will be substantially .in excess of the working voltage, but notso much as to waste space by requiring an undue margin. For example,in-the case of a condenser to workat '150/V011JS it is sufllcient if theflash-over voltage is 'as much as 300 volts. For this purpose a marginno more than ,64 Of an inch wide wouldbe sufficient, but a margin ofthis degree of narrowness is difiicult to provide by the ordinarymeans.Normally when the metal is deposited 'on the paper, the paper is maskedin such a way :as toleave thedesired edge margin, but the masking cannotproduce an extremely narrow edgemargin.

It is an object of the present invention toprovide metallised paperwhich is suitable 'for use in themanufacture of electric condensers andin which the unmetallised margins .or bands are produced withoutmaskingthe paper in the original Operational producing themetallised surface.

Although in such condensers the provision of an such-paper.

It is agfurther object of the invention to provide-metallisedpaperelectriccondensers in which the-unmetallisedportions of'the paperemployed are reduced to'the'narrowest satisfactory-dimensions,

The invention comprises a process for producing metallised paper with anunmetallised strip portion or portions thereon characterisedby firstmetallising "the paper and thereafter removing the metal from thestrip-or strips which'it is desired should be unmetallisedbybringingthema- ,terial into contact with, and moving itpast, anelectrified conductorwhile maintaining the metallised area of the paperof opposite polarity to the conductor so'that current from the conductorburns off the-metal along the saidstrip.

In one form of the process the conductor is'applied to the-unmetallisedside of thepaperalong one or both edges thereof .so that the "strip orstrips :fromwhich the metalis removed consist of one or both edgemargins ofthe paper close to'the conductor. If both edge margins arethus demetallised and the paper is of the width oftwo of the stripseventually desiredfor the condenser, it can'thereafter be slit so as toproduce two strips each having along one edgean unmetallisedmargin andalong the other edge having the metallised surface extending up to theedge. Such strips are of particular service in winding electriccondensers because the edge which has :not been demetallised isconvenient for the making of electrical, connection to a terminal, forexample as described in patent application No. 493,173.

In another'form of the process the conductor may consist ofanarrow'member of awidth suitable to produce the desired unmetallisedstrip,

applied to the paper on the metallised surface thereof. The paper insuch a case may be a web ofa width great enough to-comprise the width ofseveral unmetallised strips parallel to one another, andseveral-conductors may be applied to the metallised surfacesimultaneously so .as to produce such unmetallised strips.

The conductor or conductors may consist of a rotatable roller or rollersaround which 'the paper ispassed.

The process works best when the metallised surface'is exceedingly thinand preferably the metallised paper employed is paper on which themetallised surface has been produced by condensation of metallic vapourthereon in vacuo as an extremely thin conducting layer, forexample bythe process described in U. S. patent specifications Nos. 2,100,045 and2,153,786.

The inventionincludesa process of manufacture of electric condensersconsisting in'taking metallised paper,,producing a demetallised strip Istrips.

or strips thereon by means of steps as above described and thereafterwinding two or more strips of such paper together into an electriccondenser.

The invention further comprises apparatus for demetallising strips ofmetallised paper in which there is provided in combination means tosupport a feed-roll of metallised paper, a set of narrow demetallisingrollers supported so that the metallised face of the paper can be fedpast and in contact with them from the feed roll, means for connectingthe set of demetallising rollers to the electric supply so that theirpotential is opposite to that of the metallised face of the paper andmeans to receive paper from the demetallising roller and rewind it.

A gang of slitting knives may be set to cut the paper, before it isre-wound, along the centres of the demetallised strips and also alonglines extending along the metallised bands between the In this waystrips are obtained which are demetallised along one edge and along theother edge are metallised right up to the edge of the paper.

The following is a description, by way of example, of certain forms ofapparatus and of the process as carried out therein.

Referring to the accompanying drawings,

Figure 1 is a diagrammatic perspective view of one form of apparatus;

Figure 2 is a detail illustrating the demetallisation of the edgemargins of the paper shown in the diagram Figure 1;

Figure 3 is a plan of an alternative apparatus;

Figure 4 is a side elevation of the same.

Referring to Figure 1, I is a core on which is wound a feed roll I2 ofpaper which has been metallised on one face with an extremely thinconducting layer of aluminium or copper. The roll I2 on its core i I ismounted on a shaft I3 which is supported in bearings not shown in thedrawing. The paper is so wound on the roll I2 that the metallised faceis the inner face l4 of the paper as it comes off the roll. From theroll I2 the paper is fed past a metallic roll I5 mounted on a suitablysupported shaft I5 so that the roll I5 is in electrical contact with themetallised surface of the paper. The roll I5 is connected to thenegative or earth terminal of an electric supply as indicated by thewire I Beyond the roll I5 the paper passes upwardly and over the uppersurface of another electrical conducting roller i8 which is supportedbetween insulated point bearings i9, 29. The insulated supports for thepoint bearings are not shown in the drawings and may be of anyconstruction desired, the object being to enable the roller I8, whichforms a conductor in contact with the unmetallised surface 2| of thepaper, to be maintained (by a connection 22 to the positive terminal ofan electric supply) at a substantial potential difference from that ofthe metallised surface of the paper which is connected to the roll I5.

The potential difference applied is at least as high as that which thecondenser will eventually be called upon to bear under workin conditionsand preferably considerably higher so as to provide a margin of safety.For example, if the condenser is intended to work under a potentialdifference of 200 volts, the potential applied to the roller !8 may beof the order of 500 volts. The paper strip on the roll I2 is metallisedright up to its edges, and owing to the thinness of the paper the resultis that at the edges, as the strip reaches the conductor I8, there is aflash-over of current from the conductor to the metallised surface ofthe Paper. This flash-over burns back the metallised surface on thepaper along the margin during the passage of the paper around the rollI8, producing two demetallised edge margins 23, 24 as shown in Figure 2.If the metallisation on the paper is sufliciently thin this burning backof the edge margins will take place without appreciably carbonising thepaper itself. Thus, a demetallised edge margin of the minimum widthwhich will withstand the potential difference applied, is automaticallyproduced along each edge of the paper.

At the same time, any faults which may exist in the dielectric itselfare automatically burned out, that is to say, the metallised surface isburned away around the fault during the passage of the paper over theconductor I8 in the manner described in patent application No. 493,173.

From the conducting roller I8, the paper strip, with its twodemetallised edge margins is led past a rotating cutting knife 25 so asto be slit into two strips, each having one demetallised margin and oneedge along which the metallised surface extends up to the edge. Thestrips are wound into a roll 26, on a core 21 mounted on a suitablydriven shaft 28.

Thereafter the two rolls so produced can be used for winding into anelectrical condenser in the manner described in the aforesaidapplication No. 493,173.

By the above process an edge margin can be produced which is extremelynarrow, and, even for high voltages, as great as the paper is able tostand up to as a dielectric, may be less than 64 of an inch.

Referring now to Figures 3 and 4, the apparatus shown comprises two sideplates 3|, 32 which extend parallel to one another and in conjunctionwith suitable spacing members 33, 34 and nuts 35, 36 constitute theframe of the apparatus. On the side plates 3|, 32 at one end there aresecured brackets 31, 38 having slots 39 to receive a spindle 4|! whichcarries a feed roll 4| of metallised paper. The feed roll 4| is wound ona cardboard tube which is supported from the spindle 40 by means offlanged discs 42, 43. The flanged discs have a cylindrical portion whichfits inside the cardboard tube and a flange 44 which abuts upon itsends. The two discs are drawn together by means of three bolts 45 whichare equidistantly spaced around the spindle 48 and by knurl-headed nuts46 upon the bolts. The knurl-headed nuts do not engage the disc 43directly, but interposed between the nuts and the disc are springs 41.Thus the roll 4| is frictionally held with respect to the spindle 40 andthe tension which can be ap plied to the paper web 5| from the roll 4|is limited to the force transmissible through the frictional connection.This tends to avoid tearing the paper web, which is very thin, being ofthe order of thickness of about one-half a thousandth of an inch. Thethickness of the metallised layer upon the paper is considerably less,being less than one-fiftieth of a thousandth of an inch and themetallised layer is wound so as to face inwards on the roll and is,therefore, uppermost on the web 5| as it comes away from the roll.

Between the plates 3|, 32 there is mounted at the end nearest the roll4|, a spindle 52 carrying a roller 53. This roller is made of conductingmaterial, for example, brass, and is in electrical connection with theframe ofthe machine, which is connected to earth. Thisensuresthatthezmetall'is'ed' surface of the paper is at earthipotential.

Somewhatabove and to the rightof the spindle 5Zthere is another spindle:54 which issupported between point bearings provided by screws 55mounted inan insulating bushing 56 in removable blocks 51' in the sideplates 3t, 32 The screws 55 are electrically connected, for example bymeans of a Wire 58-; to the positive or unearthed terminal ofan electricsupply having a voltage of between 500 and 600' volts, direct current.Beyond the spindle 54 and also supported between the side plates 31 32-thereisanother spindle 60 supported in-bearing bushes 61, eachof whichworks in a vertical slot 62 in theside plate in which it is mounted. Thebearing blocks 61 are supported on springs 63 so that they tend to riseand the amount of the rise is limited by means of an adjusting screw 64in a cap plate 65. The spindle 60 carries a roller 66- over which thepaper web '51 passes. By adjusting the screws 64', the exact path of thepaper web may be adjusted within fine limits.

Upon the spindle 54' there aremounted a number of narrow disc-likeconductors 61 by means of hubs 6 8 which fit the spindle 54-. Thediameter of the conducting discs 61 is such that they just touch thepaper passing from theroller 53 to the roller 66 in the course of" itspath, and the adjustment provided by the-screws B4 is intended to ensurethat the discs 61 can engage the paper properly but without producingundue pressure upon it.

The width of theconductors 6T ismadeto correspond with the width ofstrips which it is desired should be demetallised upon the paper web 5!,and the spacing of the discs corresponds to the desired spacing betweenthe demetallised strips. It is found that as soon as the metallisedsurface of the paper touches the conductors 6'! thefiow of current atthe point of contact is suihcient to burn off and vol'ati'lise themetallised surface of thepaper, the'width so demetallised being onlyslightly greater than the width of the operative edges of the discs 61'.Consequently the paper, as it comes away fromthe discs 61, presents ametallised surface which is subdivided'by unmetallised bands, shown inthe drawing by chain lines'lfl.

Beyond the spring-supported roller 66 the paper web is caused to movedownwardly beneath a large feed roller 1| supported on a spindle 12. Thepaper web passes beneath the feed roller H into a nip provided by asecond feed roller 13 which is carried. on a shaft 1 1 mounted inbearing blocks 15. The bearing blocks 15 work in horizontal slots 16 inthe side plates 3|, 32, and they are adjustable along the slots by meansof a screw 1-! provided with adjusting nuts 18. Thus the roller 13 canbe pressed firmly against the roller H and grip the paper web securely.The shaft 14 is extended so as to provide a mounting for a drivingpulley (not shown in the drawing) and by this means'thepaper'is drawnthrough themachine at a suitable speed.

In the" stretch of the web which extends from the roller 66 to theunderside of the roller H, a slitting operation is performed upon thepaper. To this end there is" mounted in bearings 80, 8| a driven shaft82 (carrying a pulley, not shown). Upon the shaft 82 there is a gang ofcircular slitting knives 83 which are spaced apart by cylindricalspacing members 84. The knives 83 are so spaced as to slit the paperdown the centre of each of the: demetallised strips 10 andalso down thecentre-of each ofthemetallised areas between the strips. In order toensure that no lateral movement: of the slitting. knives. takes placethe gang of knives isurged by aspring toward the side plate 31. Thespring 85 is located between the bearing block 80. in the side plate 32and the end member of the spacing members 84-. At the other end of thegang of knives a thrust washer 86 is caused, by the. pressure of thespring 85, to bear on the bearing block 8|. It will be appreciated thatit is important that no lateral movement of the knives should occur asthey rotate, otherwise the paper web maybecome torn. It will also beobserved that the screws 55 which support the spindle 542 of. thedemetallising conductors 61 provide a means of adjustment so that theconductor 51 may be set exactly in line. with the slitting knives 83.Furthermore, the mounting of the feed roll 4| on the spindle 40 is suchthat the feed roll isautomatically held always in the samepositionrelatively tothe spindle, and, therefore, if the spindle 40' islifted out and a fresh roll of paper substituted when the roll in usehas become exhausted, the new roll will automatically come into the.same position relatively to the demetallising. conductors 61 and theslitting knives 83 as was the case with the previous roll. In this wayexact repetition of results is maintained.

It will, therefore, be seen that the paper web 5|, by the time ithas'passed the slitting knives 83, consists of a number of separatestrips of paper; each of which is metallised up to one edge anddemetalli ed along its other edge, the demetallised margin being equalto half the width of the demetallised strips [0. After passing the feedroller 13- the strips are separated from one another. Half of. them havedemetallised margins along. their'right-hand. edges and the other halfhave demetallised margins along their lefthand. edges. The former areled on to an upper series of re-winding rolls 90 and the latter on to alower series of re-winding rolls 9| The rolls 90 are mounted on a drivenspindle 92 and the rolls 91: on a. driven spindle 93'. These spindlesproject beyond the side plate 32 suffiiciently to carry driving pulleys,and they are driven from a driving pulley (not shown) on the spindle 14,The fragility of the paper strips makes it necessary that the forceapplied to wind them on to the rolls 90 and 91 should be strictlylimited. To this end each of the. rolls 9!] and 9l' is supported betweentwo discs 94, 95. The disc 94. has a hub by which it is mounted on thespindle (92 or 93 as the case may be) and the disc 95 is supported fromthe disc 96 by means of three equidistantly spaced bolts 91: carryingknurled nuts 98 between which and the disc. 95 there are interposedsprings 99'. The cores of the re-winding rolls 98 consist of shortcylindrical lengths I01 of cardboard tube or other suitable materialwhich are gripped between thediscs 94, 9-5 and are centred by inwardlyprojecting flanges I08: on these discs, Therefore, the driving forcewhich can be applied to the cores of the re-winding rolls is limited tothe force afforded by" the frictional grip and this can be adjusted soas to be as light as desired by means of the nuts 98*. In order toattach the ends of the paper strips- 11 tothe cores In! it is sufiicientto stick them in place with a dab of petroleum jelly or like material.

Once a web of paper has been passed through the various parts of thisapparatus and its ends appropriately attached to the re-winding rolls90, 9|, the rest of the paper can be quickly and automaticallydemetallised along the strip 70, cut by the cutting knives 85, andre-wound as a series of alternate right-handed and left-handed stripswithout necessitating undue attention on the part of the operator. Fromthe rolls 90 and 91 the paper can then subsequently be re-wound into acondenser as described, for example, in patent application No. 493,173.

It will be appreciated that if for any purpose the strips of paper arerequired to be produced With demetallised bands running down theircentre or in other positions removed from the edges, this can bearranged with apparatu of the kind illustrated in Figures 3 and 4 byappropriately spacing the discs 57 and omitting the appropriate knivesfrom the gang on the spindle 82. Of course, the re-winding rolls 90, 9|need to be arranged so as to be of appropriate breadth to receive thestrips thus produced.

I claim:

1. The method of demetallizing a selected area of that surface of astrip of very thin paper upon which there has been previously depositedan extremely thin layer of metal, which comprises continuouslymaintaining in direct contact with the exposed surface of such metallayer two spaced electrical conductors of opposite polarity one of whichmakes direct electrical contact with a relatively small area of saidsurface and the other of which makes direct electrical contact with alarger area of that surface, passing sufiicient current through saidconductors and metal layer to cause the density of the current passingdirectly between the conductor of smaller contacting area and the metallayer to be suflicientl high to cause volatilization of the metaldirectl contacted by said last mentioned conductor, and, whilemaintaining the current flow, continuously advancing the strip so as tocontinuously bring fresh areas thereof into contact with saidconductors, the speed of advancement being such that volatilization ofthe metal at the point of contact between the strip and the conductor ofsmaller strip conducting area proceeds uninterruptedl and an unbrokenelongated demetallized area is created.

2. The method of demetallizing a selected area of that surface of astrip of very thin paper upon which there has been previously depositedan extremely thin layer of metal, such metal layer being approximately000% inch in thickness but having satisfactory conducting properties,which comprises continuously maintaining in direct contact with theexposed surface of such metal layer two spaced electrical conductors ofopposite polarity one of which makes direct electrical contact with arelatively small area of said surface and the other of which makesdirect electrical contact with a larger area of that surface, passingsuificient current through said conductors and metal layer to cause thedensity of the current passing directly between the conductor of smallercontacting area and the metal layer to be sufiiciently high to causevolatilization of the metal directly contacted by said last mentionedconductor, and, while maintaining the current flow, continuouslyadvancing the strip so as to continuously bring fresh areas thereof intocontact with said conductors, the speed of advancement being such thatvolatilizaticn of the metal at the point of contact between the stripand the conductor of smaller strip conducting area proceedsuninterruptedly and an unbroken elongated demetallized area is created.

. 3. The method of demetallizing a selected area of that surface of astrip of very thin paper upon which there has been previously depositedan extremely thin layer of aluminum, which comprises continuouslymaintaining in direct contact with the exposed surface of such aluminumlayer two spaced electrical conductors. of opposite polarity one ofwhich makes direct electrical contact with a relatively small area ofsaid surface and the other of which makes direct electrical contact witha larger area of that surface, passing sufiicient current through saidconductors and aluminum layer to cause the density of the currentpassing directly between the conductor of smaller contacting area andthe aluminum layer to be sufficiently high to cause volatilization ofthe alu minum directly contacted by said last mentioned conductor, and,while maintaining the current flow, continuously advancing the strip soas to continuously bring fresh areas thereof into contact with saidconductors, the speed of advancement being such that volatilization ofthe aluminum at the point of contact between the strip and the conductorof smaller strip conducting area proceeds uninterruptedly and anunbroken elongated demetallized area is created.

The method of demetallizing a selected area of that surface of a stripof very thin paper upon which there has been previously deposited anextremely thin layer of aluminum, such aluminum layer beingapproximately .00004 inch in thickness but having satisfactoryconducting properties, which comprises continuously maintaining indirect contact with the exposed surface of such aluminum layer twospaced electrical conductors of opposite polarity one of which makesdirect electrical contact with a relatively small area of said surfaceand the other of which makes direct electrical contact with a largerarea of that surface, passing sufficient current through said conductorsand aluminum layer to cause the density of the current passing directlybetween the conductor of smaller contacting area and the aluminum layerto be sufiiciently high to cause volatilization of the aluminum directlycontacted by said last mentioned conductor and, while maintaining thecurrent flow, continuously advancing the strip so as to continuouslybring fresh areas thereof into contact with said conductors, the speedof advancement being such that volatilization of the aluminum at thepoint of contact be tween the strip and the conductor of smaller stripconducting area proceeds uninterruptedly and an unbroken elongateddemetailized area is created.

RICHARD ALFRED GROUSE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PAILNTS Number Name Date 758,923 Knowlton May 3, 1904920,970 Mansbridge May 11, 1909 1,154,301 Fogarty Sept. 21, 19151,276,731 Crowell Aug. 27, 1918 1,909,079 Steerup May 16, 1933 2,248,057Bond July 8, 1941 2,310,071 Frisch Feb. 2, 1943

